A conventional noise filter is disclosed, for example, in Japanese Laid-open Patent No. 8-335517.
FIG. 35 is a perspective exploded view of the conventional noise filter (laminated common mode choke coil). A first coil 1 and a second coil 2 formed above the first coil 1 are spirally formed, and made of silver.
An insulating sheet 3 is formed beneath the first coil 1, and is provided with two via holes 4, 5. A second insulating sheet 6 is formed between the first coil 1 and second coil 2, and is provided with one via hole 7. The first insulating sheet 3 and second insulating sheet 6 are made of insulating material such as polyimide.
A first external electrode 8 disposed at one end of the first coil 1, and a first via electrode 8a at other end of the first coil 1 are formed on the same plane as the first coil 1. A second external electrode 9 is formed beneath the first insulating sheet 3. A second via electrode 9a is formed beneath the first insulating sheet 3, and the second external electrode 9 is connected to the first via electrode 8a through the via hole 4 provided in the first insulating sheet 3, second via electrode 9a, and a first leading-out portion 10 formed beneath the first insulating sheet 3.
A third external electrode 11 provided at one end of the second coil 2, and a third via electrode ha provided at other end of the second coil 2 are formed on a same plane as the second coil 2.
A fourth external electrode 12 is provided beneath the first insulating sheet 3. A fourth via electrode 12a is formed beneath the first insulating sheet 3, and the fourth external electrode 12 is connected to the second coil 2 through the via hole 7 formed in the second insulating sheet 6, via hole 5 formed in the first insulating sheet 3, fourth via electrode 12a, and a second leading-out portion 13 formed beneath the first insulating sheet 3. That is, the second external electrode 9 and fourth external electrode 12 are formed on a same plane. The first external electrode 8, second external electrode 9, third external electrode 11, and fourth external electrode 12 are partly exposed to the end surface of the first insulating sheet 3 and second insulating sheet 6.
A specified number of third insulating sheets 14 are formed beneath the second external electrode 9 and fourth external electrode 12 and above the first coil 1, and are made of ferrite.
In this conventional noise filter, when a common mode noise is applied to the first coil 1 and second coil 2, the impedance values of the coils 1, 2 are raised, and the common mode noise is removed.
In the conventional noise filter, however, the common mode impedance cannot be raised higher.
That is, end portions of the first coil 1 and second coil 2 (the second external electrode 9 connected to the first coil 1 and fourth external electrode 12 connected to the second coil 2) are drawn out in the same direction (downward). It hence leads to possibility of short-circuiting of the via holes 5 and 7 for connecting the first via electrode 8a formed in the first coil 1, second coil 2, fourth via electrode 12a, and fourth external electrode 12. If short-circuited, the first coil 1 and second coil 2 are electrically connected, and the common mode noise removing characteristic may not be obtained. It is therefore necessary to keep a certain spacing 15 between the first via electrode 8a and via hole 7, and a conductor extending from the first coil 1 cannot be provided in this spacing 15 and the first coil 1 and second coil 2 cannot be overlaid in the area corresponding to the spacing 15, and the overlapping region of the first coil 1 and second coil 2 cannot be increased further.
Moreover, if the current flow directions are reverse in the first coil 1 and second coil 2, the magnetic fluxes generated in the first and second coils cancel each other, and the impedance of normal mode cannot be raised.
A different conventional common mode noise filter is disclosed, for example, in Japanese Utility Model Publication No. 7-45932.
FIG. 36 is a perspective exploded view of the conventional common mode noise filter (laminated coil).
In a main body 201, a first coil and a second coil are formed. Upper and lower electrodes 202 and 203 are disposed on both sides of the main body 201. Magnetic shield layers 204, 205 are provided in the outermost layer of the common mode noise filter. That is, the conventional common mode noise filter is composed of the main body 201, electrodes 202, 203, and magnetic shield layers 204, 205.
The main body 201 is composed of plural magnetic sheets for first coil 206, 207, 208, and magnetic sheets for second coil 209, 210, 211. The magnetic sheets for first coil 206 to 208 and magnetic sheets for second coil 209 to 211 are alternately disposed.
Specifically, the magnetic sheet for second coil 211, magnetic sheet for first coil 208, magnetic sheet for second coil 210, magnetic sheet for first coil 207, magnetic sheet for second coil 209, and magnetic sheet for first coil 206 are laminated sequentially from the bottom.
On the top of the magnetic sheets 206 to 211, conductor patterns for forming the first coil 212, 213, 214, and conductor patterns for forming the second coil 215, 216, 217 are printed in a square shape of nearly one turn.
A terminal end 212b of the conductor pattern 212 formed in the magnetic sheet 206 is electrically connected to an initial end 213a of the conductor pattern 213 formed in the magnetic sheet 207 by way of a through-hole 212c of the terminal end 212b and a through-hole 209a of the magnetic sheet 209.
Also, a terminal end 213b of the conductor pattern 213 formed in the magnetic sheet 207 is electrically connected to an initial end 214a of the conductor pattern 214 formed in the magnetic sheet 208 by way of a through-hole 213c of the terminal end 213b and a through-hole 210a of the magnetic sheet 210.
Similarly, a terminal end 215b of the conductor pattern 215 formed in the magnetic sheet 209 is electrically connected to an initial end 216a of the conductor pattern 216 formed in the magnetic sheet 210 by way of a through-hole 215c of the terminal end 215b and a through-hole 207a of the magnetic sheet 207.
Further, a terminal end 216b of the conductor pattern 216 formed in the magnetic sheet 210 is electrically connected to an initial end 217a of the conductor pattern 217 formed in the magnetic sheet 211 by way of a through-hole 216c of the terminal end 216b and a through-hole 214a of the magnetic sheet 208.
In this way, the first coil composed of conductor patterns 212 to 214 of magnetic sheets 206 to 208, and the second coil composed of conductor patterns 215 to 217 of magnetic sheets 209 to 211, in the same phase and same number of turns as the first coil, are formed in every other layer.
The upper electrode 202 is composed of magnetic sheets 218, 219, and 220. On the magnetic sheets 218 to 220, leading-out electrode conductor patterns 221a, 221b, 221c, 222a, 222b, 222c are formed respectively.
The leading-out electrode conductor patterns 221a to 221c are mutually connected by way of through-hole, and are further connected with the initial end 212a of the conductor pattern 212 of the magnetic pattern 206 for forming the first coil.
Similarly, the leading-out electrode conductor patterns 222a to 222c are mutually connected by way of through-hole, and are further connected with the initial end 215a of the conductor pattern 215 of the magnetic pattern 209 for forming the second coil.
In this manner, on the upper electrode 202, a first coil leading-out electrode terminal T1a, and a second coil leading-out electrode terminal T2a are formed.
Further, the lower electrode 203 is composed of magnetic sheets 223, 224, and 225. On the magnetic sheets 223 to 225, leading-out electrode conductor patterns 226a, 226b, 226c, 227a, 227b, 227c are formed respectively. (227b, 227c are not shown.)
The leading-out electrode conductor patterns 226a to 226c are mutually connected by way of through-hole, and are further connected with the terminal end 214b of the conductor pattern 214 of the magnetic pattern 208 for forming the first coil.
Similarly, the leading-out electrode conductor patterns 227a to 227c are mutually connected by way of through-hole, and are further connected with the terminal end 217b of the conductor pattern 217 of the magnetic pattern 211 for forming the second coil.
In this manner, on the lower electrode 203, a first coil leading-out electrode terminal T1b, and a second coil leading-out electrode terminal T2b are formed.
In this conventional common mode noise filter, when a common mode noise is applied in the first coil and second coil, the impedance values of the coils are raised, and the common mode noise is removed.
In the conventional common mode noise filter, however, the common mode impedance cannot be raised further.
That is, of the square-shaped conductor patterns 212 to 217, for example relating to the pattern 212 for composing the first coil, since the initial end 212a is formed inside of the terminal end 212b, the conductor pattern between the initial end 212a and the folded portion 212d of the conductor pattern 212 cannot be overlaid on the conductor pattern 215 for forming the second coil in the top view, and therefore the magnetic flux generated by the first coil and the magnetic flux generated by the second coil cannot reinforce each other efficiently.